1. Field of the Invention
The present invention relates to a micro movable element, such as a micromirror or a gyro sensor, that includes a pivotable unit. The present invention also relates to an optical switching device that incorporates a micromirror constituted as a micro movable element.
2. Description of the Related Art
In various industrial fields, minute devices manufactured by a micromachining technology are widely used. In the field of the optical communication for example, attention is drawn to minute micromirror devices with desired optical reflectivity. As another example, in the field of sensing techniques, gyro sensors are widely utilized for providing inertial sensors, car navigation systems and on-board airbags, or for performing robot posture control or prevention of blurring images due to hand movement in taking pictures.
In the optical communication in which optical signals are transmitted via optical fibers, optical switching devices are generally employed for switching the transmission route of the optical signal from a fiber to another. Characteristics required from the optical switching device for achieving excellent optical communication performance include large capacity, high speed, and high reliability in the switching operation. From such a viewpoint, optical switching devices including micromirror devices manufactured by the micromachining technique are very popular. This is mainly because the micromirror device eliminates the need to convert the optical signal into an electrical signal between the input-side optical line and the output-side optical line in the optical switching device, thereby facilitating achieving the required characteristics. The micromachining technique is disclosed in, for example, patent documents 1 to 3 listed below.                Patent document 1: JP-A-H10-190007        Patent document 2: JP-A-H10-270714        Patent document 3: JP-A-2000-31502        
FIG. 17 depicts an outline of a popular optical switching device 60. The optical switching device 60 includes a pair of micromirror arrays 61, 62 and a plurality of micro lenses 63, 64, and is disposed between an input fiber array 71 and an output fiber array 72. The input fiber array 71 includes a number of input fibers 71a, and the micromirror array 61 includes a plurality of micromirror units 61a respectively corresponding to each input fibers 71a. Likewise, the output fiber array 72 includes a predetermined number of output fibers 72a, and the micromirror array 62 includes a plurality of micromirror units 62a respectively corresponding to each output fiber 72a. The micromirror units 61a, 62a respectively include a pivotably installed movable unit with a mirror surface for light reflection, and an actuator that generates a driving force for the pivotal motion of the movable unit, so as to control the orientation of the mirror surface of the movable unit. The micro lenses 63 are respectively disposed so as to face the facet of the input fibers 71a. Likewise, the micro lenses 64 are respectively disposed so as to face the facet of the output fibers 72a. 
In an optical transmission, light L1 emitted from the input fiber 71a turns into mutually parallel light upon passing through the micro lens 63, and advances toward the micromirror array 61. The light L1 is reflected by the mirror surface of the micromirror unit 61a, and thus deflected toward the micromirror array 62. At this moment, the mirror surface of the micromirror unit 61a is oriented to a predetermined direction in advance, so as to make the light L1 incident upon a desired micromirror unit 62a. Then the light L1 is reflected by the mirror surface of the micromirror unit 62a, and thus deflected toward the output fiber array 72. At this moment, the mirror surface of the micromirror unit 62a is oriented to a predetermined direction in advance, so as to make the light L1 incident upon a desired output fiber 72a. 
Thus in the optical switching device 60, the light L1 emitted from the input fiber 71a reaches the desired output fiber 72a through the deflection by the micromirror arrays 61, 62. This achieves one-to-one optical connection between the input fiber 71a and the output fiber 72a. Accordingly, appropriately adjusting the deflection angle of the micromirror unit 61a, 62a can switch the output fiber 72a which the light L1 is to reach.
FIG. 18 depicts an outline of another popular optical switching device 80. The optical switching device 80 includes a micromirror array 81, a fixed mirror 82 and a plurality of micro lenses 83, and is disposed so as to confront an input/output (hereinafter, I/O) fiber array 90. The I/O fiber array 90 includes a predetermined number of input fibers 91 and a predetermined number of output fibers 92, and the micromirror array 81 includes a plurality of micromirror units 81a respectively corresponding to each fiber 91, 92. The micromirror units 81a respectively include a pivotably installed movable unit with a mirror surface for light reflection, and an actuator that generates a driving force for the pivotal motion of the movable unit, so as to control the orientation of the mirror surface of the movable unit. The micro lenses 83 are respectively disposed so as to face the facet of the fibers 91, 92.
In an optical transmission, light L2 emitted from the input fibers 91a advances toward the micromirror array 81 through the micro lenses 83. The light L2 is reflected by the mirror surface of a corresponding first micromirror unit 81a, and thus deflected toward the fixed mirror 82, by which the light L2 is reflected and thus deflected toward a corresponding second micromirror unit 81a. At this moment, the mirror surface of the first micromirror unit 81a is oriented to a predetermined direction in advance, so as to make the light L2 incident upon a desired second micromirror unit 81a. Then the light L2 is reflected by the mirror surface of the second micromirror unit 81a, and thus deflected toward the I/O fiber array 90. At this moment, the mirror surface of the second micromirror unit 81a is oriented to a predetermined direction in advance, so as to make the light L2 incident upon a desired output fiber 92.
Thus in the optical switching device 80, the light L2 emitted from the input fiber 91 reaches the desired output fiber 92 through the deflection by the micromirror arrays 81 and the fixed mirror 82. Accordingly, appropriately adjusting the deflection angle of the first and the second micromirror unit 81a can switch the output fiber 92 which the light L2 is to reach.
In an existing optical switching device in general, the micromirror array is constituted of a plurality of micromirror units integrally formed in a single substrate (micromirror substrate) and fixed on an interconnect substrate, and then mounted on a package base via the interconnect substrate. The interconnect substrate is provided, on the same surface where the micromirror substrate is provided, with an interconnect pattern including a predetermined number of electrode pads (first electrode pad) located in a periphery of the substrate, and the interconnect pattern is electrically connect to the actuator of the respective micromirror units in the micromirror substrate. The package base includes a predetermined interconnect structure including a predetermined number of electrode pads (second electrode pad) formed on the same surface as the micromirror substrate or the interconnect substrate, and the interconnect structure and the interconnect pattern on the interconnect substrate are electrically connected by wire bonding between the first electrode pad and the second electrode pad. Such micromirror substrate, interconnect substrate and package base constitute a micromirror device to be implemented on a mother board or the like.
In the existing optical switching device or micromirror device thus structured, an increase in the number of fibers resultant from expansion of the optical communication network leads to an increase by the same extent in the number of micromirror units or movable units with the mirror surface to be included in a single micromirror substrate. The increase in the number of movable units in turn complicates the routing arrangement of the interconnect pattern on the interconnect substrate necessary for driving all the movable units, thereby increasing the dimensions of the interconnect substrate. Such complication of the routing arrangement of the interconnect pattern and the increase in dimensions of the interconnect substrate are unfavorable, especially from the viewpoint of cost efficiency in manufacturing the micromirror device, and hence the optical switching device. Further, the more movable units are introduced, the more first electrode pads have to be provided in the interconnect substrate and the more second electrode pads in the package base, which naturally results in an increase by the same extent in the wire bonding steps to connect the first electrode pad and the second electrode pad. The increase in the wire bonding steps is undesirable in improving the yield of the production of the micromirror device or the optical switching device. Thus, the conventional technique still has a room for improvement, to carry out efficient production of the micromirror device or the optical switching device.